JERUSALEM, Israel -- Satellite images of Iran's Parchin military facility show two side buildings completely removed, raising speculation of destroying evidence of nuclear weapons research at the site.

Reuters reports that the Institute for Science and International Security (ISIS), a think tank that follows Iran's nuclear program closely, posted images on its website from May 25, shortly after IAEA officials in Vienna examined similar images during a security briefing in Vienna.

"Heavy machinery tracks and extensive evidence of earth displacement is also visible throughout the interior, as well as the exterior of the site's perimeter," ISIS said on its website.

Iran has repeatedly refused to allow IAEA inspectors access to the site.

But ISIS says Iran is "sanitizing" the site before it allows IAEA inspectors there, noting that images taken in early April show the buildings, which have been "completely razed," intact.

"Heavy machinery tracks and extensive evidence of earth displacement is also visible throughout the interior as well as the exterior of the site's perimeter," the security firm says.

A report issued by the IAEA last week noted "extensive activities" at the site.

"The newest image raises concerns that Iran is attempting to raze the site prior to allowing an IAEA visit. The razing of the two buildings may also indicate that Iran has no intention to allow inspectors access soon," ISIS said.

An IAEA report issued last November said a large containment vessel built in 2000 may be used for test explosives, which officials say are "strong indicators of possible [nuclear] weapon development."

According to the report, one of the buildings housed a large cylindrical structure, which officials believe was used for testing up to 70 kilograms (about 35 pounds) of explosive material as much as a decade ago.